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340                   LIGHT MINERAL OILS  (BENZINE)

Crude petroleums have specific gravities varying from 0-771 to about 1-020,
the Russian being usually denser than the American.

As regards fractional distillation, good American crude petroleums generally
contain much light oil and lamp oil, while their heavy fractions contain marked
quantities of solid paraffin. Russian petroleums, however, furnish less quan-
tities of light and middle distillates, whilst the heavy fractions abound, although
these are poor in paraffin wax. Galician and Rumanian petroleums are mostly
rich in middle fractions, and their heavy ones contain solid paraffin. Italian
petroleums are usually richer in light and middle than in heavy fractions.

The flash point is mostly near o°, but varies with the content of light oils.

The sulphur content is generally low (less than i%), but in some cases, e.g.,
in Texan and Californian petroleums, more is found (4-5%).

The calorific power of crude petroleums is as a rule 10,000-11,000 cals. and
diminishes as the specific gravity increases. Petroleums poor in the lighter
fractions are more particularly used directly as fuels, e.g., those of Texas, Cali-
fornia and Mexico ; petroleums with little sulphur are preferable for this pur-
pose, but those with larger proportions may also be used.



These are volatile, mobile, colourless, or pale yellow liquids, usually
clear "but sometimes opalescent, in which case the presence of water is to
be suspected.

The following tests and determinations are made :

1.  Determination of the Specific Gravity.—This is made at 15°
by the methods indicated for crude petroleum.

For fiscal purposes the Italian Customs authorities use two thermo-
aerometers, one for the densities 0-610-0-760 and the other for 0-680-0-770.
By means of tables published on the authority of the Ministry of Finance,1
density readings made at other temperatures are reduced to 15°. If the
weight of any consignment is known, the volume can then be calculated.

Besides as a means of characterising the various products comprised under
the name light petroleum oils, the specific gravity may serve as an indication
of the presence of benzoles, oil of turpentine or light resin oils, all of these having
much higher specific gravities—0-86 or more.

2.  Distillation.—Use is made of the flask already described for crude
petroleum, this being connected with a good condenser and heated on a
sand-bath with a lamp the flame of which is completely enclosed in a wire
gauze cage, so that ignition of the vapours in case the flask breaks may
be avoided.

The temperature at which the distillation commences is noted and the
distillate collected either in a graduated cylinder, the volume for each 10°
being observed, or in a separate tared vessel for each fraction, the vessel
being afterwards reweighed. If the whole of the liquid does not distil
over below 150°, the distillation is stopped at this temperature and the
residue in the flask weighed.

1 Tables for the determination of the density and volume at 15° of mineral oils,
Rome, 1912. the difference representing the quantity of asphalt and